1. Field of the Invention
The invention relates generally to the coexistence between a plurality of wireless communications modules, and more particularly, to systems and methods for the reducing interference between a plurality of co-existed wireless communications modules.
2. Description of the Related Art
To an increasing extent, a multitude of communication functions are being merged into mobile devices. As shown in FIG. 1, a cellular phone may connect to a wireless local area network (WLAN) via a Wireless Fidelity (WiFi) module thereof and simultaneously communicate with a Bluetooth (BT) handset (or a Bluetooth car audio, or others) through a Bluetooth module thereof. A WLAN system is typically implemented inside buildings as an extension to wired local area networks (LANs) and is able to provide the last few meters of connectivity between a wired network and mobile or fixed devices. According to the IEEE 802.11 standard, most WLAN systems may operate in the 2.4 GHz license-free frequency band and have very low throughput rates because of the coexistence interference from BT. Referring to FIG. 1, a WLAN is established by an access point (AP) connecting to a LAN by an Ethernet cable. The AP typically receives, buffers, and transmits data between the WLAN and the wired network infrastructure. The AP may support, on average, twenty devices and have a coverage varying from 20 meters in an area with obstacles (walls, stairways, elevators etc) to 100 meters in an area with clear line of sight. Bluetooth is an open wireless protocol for exchanging data over short distances from fixed and mobile devices, creating personal area networks (PANs). The cellular phone may receive the voice over internet protocol (VoIP) data via the WiFi module and further transmit the VoIP data through an established PAN to the Bluetooth handset, and vice versa. Alternatively, the cellular phone may transmit digital music through the established PAN to be played back in the Bluetooth handset. The WLAN and Bluetooth systems both occupy a section of the 2.4 GHz Industrial, Scientific, and Medical (ISM) band, which is 83 MHz-wide. Due to cost issues as well as space requirements for components, modern electronic devices, such as cellular phones, Ultra-Mobile PCs (UMPCs) or others, are equipped with WiFi and Bluetooth modules sharing a single antenna instead of multiple antennas.
As an example shown in FIG. 2, a Bluetooth system uses a Frequency Hopping Spread Spectrum (FHSS) and hops between 79 different 1 MHz-wide channels in a Bluetooth spectrum. A WLAN system uses a Direct Sequence Spread Spectrum (DSSS) instead of a FHSS. A WLAN system carrier remains centered on one channel, which is 22 MHz-wide. When the WiFi module and the Bluetooth module are operating simultaneously in the same area, as shown in FIG. 1, the single WLAN channel, which is 22 MHz-wide, occupies the same frequency space as 22 out of 79 Bluetooth channels which are 1 MHz-wide. When a Bluetooth transmission occurs on a frequency band that falls within the frequency space occupied by an ongoing WLAN transmission, a certain level of interference may occur, depending on the signal strength thereof. Due to the fact that the WiFi module and Bluetooth module share the same spectrum and also share a single antenna, avoiding interference therebetween is required.
FIG. 3 is a diagram illustrating an operation conflict which may occur between a WLAN and a Bluetooth communication services sharing a single antenna. In FIG. 3, the shared single antenna is switched between WLAN and Bluetooth communication services in a given time slot for transceiving data. If the Bluetooth communication service carries audio data that requires real-time transmission, for example, the Synchronous Connection-Oriented (SCO) packets, the Bluetooth communication service would have a higher priority over the WLAN communication service. In this case, when a WLAN transceiving process takes place at the same time as the real-time Bluetooth transceiving process, the time slot will be assigned to the Bluetooth transceiving process and the WLAN transceiving process will be blocked. As shown in FIG. 3, the WLAN receiving operation (Rx operation) 1 occurs in the time slot, while the Bluetooth communication service is idle. Therefore, the Rx operation 1 is performed without interference and an acknowledgement (ACK) message 2 is sent to the WLAN AP (such as the AP in FIG. 1) as a reply message indicating that the Rx operation 1 is finished. Following the Rx operation 1, another WLAN Rx operation 3 is performed. The Rx operation 3 is also performed without interference because the Bluetooth communication service is in the idle state. However, an ACK message 4 in response to the Rx operation 3 can not be replied to the WLAN AP, as its time slot is already assigned to the Bluetooth transmitting operation (Tx operation). Accordingly, the Rx operation 3 would be determined to have failed. In response to the failure, the WLAN AP would re-sent the data with a lower data rate in an attempt to successfully transmit data to the WLAN module of the mobile device. Unfavorably, the re-performed Rx operation 3 (denoted as 5), with a prolonged operation period, will be more likely to overlap with the Bluetooth transceiving process. Another data re-sent with a lower data rate than that of the prior re-sent would be further attempted, causing more overlap with the Bluetooth transceiving process than the prior attempt. As a result, WLAN throughput is highly damaged as the WLAN and Bluetooth wireless communication services sharing a single antenna.